This has been discussed multiple times: https://japanese.stackexchange.com/questions/21318/what-is-being-abbreviated-as-%e3%81%a3%e3%81%a1%e3%82%83%e3%81%82-in-%e5%bf%99%e3%81%97%e3%81%84%e3%81%a3%e3%81%a1%e3%82%83%e3%81%82%e5%bf%99%e3%81%97%e3%81%84%e3%81%91%e3%81%a9/21367#21367
– Aug 22 '17 at 00:26